1. Field of the Invention
The present invention relates to a security device for conveying systems with unmanned vehicles. More specifically, this invention is directed to a security device for detecting objects in the path of an unmanned vehicle or persons entering a certain area which is reserved for vehicles only.
2. Description of the Prior Art
Conventional security devices for preventing unmanned vehicles to collide with objects (e.g. persons), usually consist of mechanical constructions protruding on the exterior of the vehicle and covering at least the width of its path (such as bumpers). Deformation of this security device causes an emergency stop of the vehicle.
In conveying systems, transport vehicles have to cooperate with stationary support structures, in order to pick up or deposit their load. Yet, very often such cooperation has proved difficult or even impossible since the security device collides with these support structures before the vehicle is close enough to the latter. Adapting the construction of the support structures is not always possible or would result in other shortcomings.
In such cases, the aforementioned security devices have to be deactivated, which usually entails closing of the load delivery areas for all other traffic, especially persons. Often however, this is incompatible with the idea of the conveying system, which, e.g. in the case of flexible assembly lines, consists precisely in a close linkage of automatic transport and manual work.
Other conventional solutions, such as proposed by DE-A 3 501 598, wherein persons working in the conveying area wear helmets or/and belts with integrated infrared emitters and the vehicles are equipped with corresponding infrared detectors, bear apparently similar shortcomings regarding the desirable close linkage man/vehicle.
In automatic conveying systems it is further required that certain areas, paths or places used by unmanned vehicles are provided with security systems which cause the traffic to stop if a person enters the protected area.
Generally known security devices of this kind comprise several stationary light barriers in succession. The distance between the first and the last of these light brriers is chosen such that a vehicle is capable of interrupting all of them at the same time, whereas persons are detected because they interrupt only a limited number of related light barriers.
Yet such a security device is not capable of detecting a person walking at the side of a vehicle or carrying an object of about the length of a vehicle (e.g. a board or a plate).